Method and apparatus for filling containers with piece goods

ABSTRACT

In a method of filling containers with piece goods, the piece goods are fed on a feed conveyer to at least two robots arranged in the conveying direction, in order by means of these robots to be put into empty spaces in the containers conveyed on a container conveyer. In the process, the robots are controlled in accordance with the arrangement of the piece goods on the feed conveyer, in such a way that they are utilized at least approximately uniformly. As a result, the lifetime of the robots may be increased.

TECHNICAL FIELD

[0001] The invention relates to a method and an apparatus for fillingcontainers with piece goods.

PRIOR ART

[0002] For packaging systems, it is known to put piece goods, which aredelivered to a packaging station via feed conveyors, into containers bymeans of robots. EP-A-0 250 470 discloses robots of this type, alsoreferred to as pickers, which are suitable for use in packaging lines.What is concerned here is a robot arm with a base element, to which anoperating part is attached via three two-part arms and on which in turngrippers or suction elements are arranged.

[0003] Primarily when the piece goods are supplied with irregularspacing and unordered, optical detection systems are used in order toregister the position and alignment of the individual piece goods on thefeed conveyor, as disclosed in U.S. Pat. No. 5,186,599, for example.This data is transmitted to a robot control system, which controls theindividual robots appropriately in order to put as many of the piecegoods as possible into the container. In the process, the first robot inthe conveying direction will grip as many piece goods as possible andthe following robots will attempt to remove the remainder from the feedconveyor.

[0004] However, this leads to the individual robots being utilized todifferent extents. The first robot in the conveying direction has ahigher operating loading than the last in the series. In addition, allthe robots are subjected to wide output fluctuations, as can be seenfrom FIG. 1. This illustrates the number of products which are grippedper second by a robot. These values are indicated for a total of fourrobots, the individual robots being numbered in the conveying direction.This means that robot number 1 is the first robot in the conveyingdirection. As can be seen in FIG. 1, the first two robots always operateat their maximum output limit. The third robot frequently reaches itsoutput limit, but also exhibits wide fluctuations in the operatingloading. The fourth robot, by contrast, is hardly utilized, but issubject to massive output fluctuations.

[0005] This distribution of the operating loading has the disadvantagethat robots which always operate at their output limit or which aresubjected to wide fluctuation have a shortened lifetime because of thehigh mechanical stress.

SUMMARY OF THE INVENTION

[0006] It is therefore an object of the invention to specify a methodand an apparatus which increases the lifetime of the individual robots.

[0007] This object is achieved by a method and an apparatus having thefeatures of patent claim 1 and 7, respectively.

[0008] According to the invention, the robots are driven in such a waythat all the robots are utilized as uniformly as possible over time andare not subjected to any wide output fluctuations. This leads to all therobots being in at least approximately the same output range, the outputrange lying underneath a maximum output range. In a preferred variant ofthe method, not only are the robots driven appropriately, but the speedof the container conveyer is also controlled.

[0009] Further advantageous embodiments emerge from the dependent patentclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] In the following text, the subject matter of the invention willbe explained by using a preferred exemplary embodiment, which isillustrated in the attached drawings, in which:

[0011]FIG. 1 shows a graphical representation of the time loading of arobot system according to the prior art;

[0012]FIG. 2 shows a graphical representation of a product stream as afunction of time;

[0013]FIG. 3 shows a schematic representation of a packaging systemhaving a feed conveyer and a plurality of robots;

[0014]FIG. 4 shows a flowchart of the method according to the invention;

[0015]FIG. 5 shows a schematic representation of a model on which themethod according to the invention is based and

[0016]FIG. 6 shows a graphical representation of the time loading of arobot system according to the invention.

WAYS OF IMPLEMENTING THE INVENTION

[0017]FIG. 2 illustrates a product stream of piece goods S, such astypically occurs on a feed conveyer 1 of a packaging system. The productstream exhibits wide fluctuations over time. The piece goods S can beconveyed in an ordered or unordered manner.

[0018] As FIG. 3 illustrates, the piece goods S can be gripped by robotsR1, R2, R3 arranged in the conveying direction and deposited incontainers B, which are likewise transported on a conveyer, a containerconveyer 2. Three robots are illustrated here. However, the methodaccording to the invention is suitable for robot systems having 2 to nrobots, n being a natural number. In this case, these are preferably thepicker robots mentioned at the beginning.

[0019]FIG. 3 illustrates conveyance on the cocurrent principle. Thismeans that the containers B move in the same direction as the piecegoods S. However, the method according to the invention can also be usedin packaging systems which have a counter current, a cross current oranother type of conveyance of the piece goods S and the containers B.

[0020] In the method according to the invention, the objective isfollowed of filling all the containers B completely, but in the processloading the robots R1 to R3 or Rn as uniformly as possible over time. Inthis case, filling the containers B has the first priority, clearing allthe piece goods S from the feed conveyer has the second priority.

[0021] In order to control the robots R1 to Rn, a robot control systemRS has to know the state of the system before each calculation time. Forthis purpose, there is an optical detection system O upstream of therobots R1 to Rn in the conveying direction, which detects the positionand alignment of the individual piece goods and forwards this data tothe robot control system RS as state variables. Further state variableswhich are taken into account by the robot control system RS are thespeed of the feed conveyer 1 and the dynamic behavior of the stream ofholes. The holes are the number of free spaces to be filled in thecontainers B. The dynamic behavior contains both the number and thespeed of movement on the container conveyer 2. All these state variablesare measured before the calculation of the area of use of the individualrobots. Furthermore, the robot control system has information relatingto the individual robots, such as their maximum loading capacity andtheir fitness for use. The speed of the container conveyer 2 is alsopresent as a control variable.

[0022] In the method according to the invention, the current robotoutput and, preferably, also the speed of the container conveyer iscalculated in such a way that the following secondary conditions arefulfilled:

[0023] the output of each robot must be less than or equal to themaximum output;

[0024] the output of each robot must be less than or equal to theproduct stream before the respective area of use, the so-called robotcell;

[0025] the robot output must not lead to robots attempting to pack morepiece goods than there are free spaces in a container;

[0026] the minimum robot output must be such that the following robotcells still fill the remaining empty spaces in the containers;

[0027] the output of the first and of the last robot cell and the speedof the container belt must be such that all the containers are filledand

[0028] the output of the first and of the last robot cell must be suchthat the following robot cells as far as possible manage a large part ofthe remaining product stream.

[0029] The set of all physically practical solutions is restricted bythe abovementioned secondary conditions. Of course, still furthersecondary conditions could be formulated. By using FIG. 4, it can beseen how the robot control system generates solutions and tests whetherthese fulfill the abovementioned secondary conditions. Those solutionswhich fulfill the secondary conditions are assessed, taking theabovementioned objective into account, and are assigned a ranking. Afterall the practical solutions have been generated, those are selectedwhich best fulfill the preset objectives, that is to say which fill thecontainers most completely but load the robots most uniformly.

[0030] The method according to the invention operates with time units,the steps listed below being carried out within one unit. The controlvariables from the last time unit are stored in order to calculate thesecondary conditions. The length of a time unit depends on the type ofpackaging system. Typical values are around 3 seconds for one unit.

[0031] In a first step A, the state variables are determined ormeasured. In a second step B, physically practical solutions aregenerated which, in a third step C, are checked for the secondaryconditions. If the latter are not fulfilled, then step B is repeated. Ifthe secondary conditions are fulfilled then, in a fourth step D, thesolution is assessed on the basis of the objective and stored in a fifthstep E, the process being continued at step B. Once all thepossibilities have been exhausted, then, in a sixth step F, the bestsolution is removed from the store and used as the control variable SV,in order to control the robots R1 to Rn and also the container conveyeruntil the next time unit.

[0032] In the following text, the individual steps will be explained inmore detail:

[0033] In the second step B, physically possible solutions aregenerated. This is done, for example, by discretizing the possible robotoutputs between 0 and a maximum output and generating all the possiblecombinations of the individual robot outputs. As FIG. 5 illustrates, thesystem is based on the principle of maintaining the mass of the productsin each robot cell. FIG. 5 illustrates a plurality of successive cells,y_(i−1)(k) piece goods being conveyed into the ith robot cell, u_(i)(k)piece goods being put into the container by the robot, y_(i)(k) piecegoods leaving the ith robot cell again. Also illustrated is the holestream, that is to say the free spaces in the containers. z_(i−i)(k)holes pass into the ith robot cell, z_(i)(k) leave it again. b is thehole stream which enters the system at the start. Therefore, on the onehand, the following is true of the maintenance of mass for the piecegoods, which is represented in a first system of equations, the massmaintenance system of equations:

y _(i+1)(k+1)=y _(i)(k)−u _(i+1)(k)

z _(i)(k+1)=z _(i−1)(k)−u _(i+1)(k)+Δb(k)

Δb(k)=b(k)−b(k−1)

[0034] On the other hand, for a system having n robot cells, at the timek in a second system of equations, the following is true, thetime-discrete dynamic system of equations:

y ₁(k+1)=p(k)−u ₁(k)

Y ₂(k+1)=y ₁(k)−u ₂(k)

y _(i)(k+1)=y _(i−1)(k)−u _(i)(k)

y _(n)(k+1)=y _(n−1)(k)−u _(n)(k)

z ₁(k+1)=u _(n+1)(k)−u ₁(k)

z ₂(k+1)=z ₁(k)−u ₂(k)+u _(n+1)(k)−z _(n+1)(k)

z _(i)(k+1)=z _(i−1)(k)−u _(i)(k)+u _(n+1)(k)−z _(n+1)(k)

z _(n)(k+1)=z _(n−1)(k)−u _(n)(k)+u _(n+1)(k)−z _(n+1)(k)

z _(n+1)(k+1)=u _(n+1)(k)

[0035] Here, u_(n+1) represents the hole stream which enters the systemat the start. By selecting the speed of the container conveyer, theinitial hole stream can be controlled. If the containers are arranged onthe container conveyer at equal intervals, then the initial hole streamis linked linearly with the belt speed.

[0036] At the time k, it is therefore possible to calculate thevariables u and to define the robot output, in order to define the stateof the system unambiguously at the time k+1. The movement of the productstream from one robot cell to the next may be described by means of theequation y_(i)(k+1)=y_(i−1)(k)−u_(i)(k).

[0037] This is similarly true for the hole stream.

[0038] Step C is preferably carried out in the form of a negativeselection, in that a test is performed to see whether the secondaryconditions are violated. If this is not the case, the method proceeds tothe next step D.

[0039] In the fourth step D, the solution is assessed by using theobjective. This can be achieved in an extremely wide range offormulations, such as by means of variance of the individual robotoutputs or the sum of the difference of the individual robot outputs andthe average of the outputs.

[0040] The steps B-D are preferably formulated as an optimizationproblem, which is solved by means of quadratic programming. In thiscase, use is preferably made of the Lemke algorithm or a generalizedinternal point method. The quality of a solution is assessed by means ofa quadratic target function, and the secondary conditions result in aset of solutions restricted by linear equations. However, otheralgorithms can also be used for this purpose, for example dynamic orgeneral nonlinear programming can be used.

[0041]FIG. 6 illustrates how the individual robots are loaded in themethod according to the invention. As can be seen in comparison withFIG. 1, the individual robots are utilized more uniformly, there arehardly any peaks any more, and all the robots are loaded approximatelyequally, none operating in the maximum output range. List ofdesignations S Piece goods R1 - Rn Robots B Containers n Natural number1 Feed conveyer 2 Container conveyer RS Robot control system SV Controlvariable O Optical detection system A First step B Second step C Thirdstep D Fourth step E Fifth step F Sixth step

1. A method of filling containers (B) with piece goods (S), the piecegoods (S) being fed on a feed conveyer (1) to at least two robots (R1 .. . Rn) arranged in the conveying direction, in order by means of theserobots to be put into empty spaces in the containers (B) conveyed on acontainer conveyer (2), the robots (R1 . . . Rn) being controlled inaccordance with the arrangement of the piece goods (S) on the feedconveyer (1), wherein the robots (R1 . . . Rn) are driven in such a waythat they are utilized at least approximately uniformly over time. 2.The method as claimed in claim 1, wherein the speed of the containerconveyer (2) is controlled in order to control the loading of the robots(R1 . . . Rn).
 3. The method as claimed in claim 1, wherein the fillingoperation is subdivided into time units (k), wherein state variables aredetermined for each time unit (k), wherein the maintenance of the numberof piece goods during filling is represented in a first system ofequations, wherein the dynamic behavior of the free spaces and of thepiece goods during a time unit are represented in a second system ofequations, wherein complete filling of the containers and utilization ofall the robots uniformly over time are introduced as boundaryconditions, wherein a time-discrete dynamic system of equations is setup and, by means of optimization algorithms and taking into account theboundary conditions and the state variables, the best parameters forcontrolling the robots are determined.
 4. The method as claimed in claim3, wherein quadratic programming is used for the optimization.
 5. Themethod as claimed in claim 3, wherein the state variables comprise thearrangement, number and alignment of the piece goods on the feedconveyer and the maximum output of the individual robots.
 6. The methodas claimed in claim 1, wherein the system is subdivided into time units(k), wherein state variables are determined for each time unit (k),wherein at least approximately all the physically possible solutions aregenerated for each time unit, wherein secondary conditions are checked,wherein solutions are evaluated by using an objective, wherein thesolutions are compared with one another and wherein the best solution isused as a control variable for controlling the robots in this time unit.7. An apparatus for filling containers (B) with piece goods (S), itbeing possible for the piece goods (S) to be fed on a feed conveyer (1)to at least two robots (R1 . . . Rn) arranged in the conveying directionand, by means of these robots (R1 . . . Rn), put into empty spaces inthe containers (B) conveyed on a container conveyer (2), the robots (R1. . . Rn) being controllable in accordance with the arrangement of thepiece goods (S) on the feed conveyer (1), wherein there is a robotcontrol system (RS) by means of which the robots (R1 . . . Rn) can bedriven in such a way that they are utilized at least approximatelyuniformly over time.
 8. The apparatus as claimed in claim 7, wherein theapparatus has a detection unit (O) which is connected to the robotcontrol system and by means of which the number and arrangement of thepiece goods can be registered.
 9. The apparatus as claimed in claim 7,wherein the speed of the container conveyer can be controlled by meansof the robot control system for the purpose of optimizing the uniformutilization of the robots.